Parsing timestamps from string and rounding seconds in spark - apache-spark

Question

I have a spark DataFrame with a column "requestTime", which is a string representation of a timestamp. How can I convert it to get this format: YY-MM-DD HH:MM:SS, knowing that I have the following value: 20171107014824952 (which means : 2017-11-07 01:48:25)?
The part devoted to the seconds is formed of 5 digits, in the example above the seconds part is = 24952 and what was displayed in the log file is 25 so I have to round up 24.952 before applying the to_timestamp function, that's why I asked for help.

Answer 1

Assuming you have the following spark DataFrame:
df.show()
#+-----------------+
#| requestTime|
#+-----------------+
#|20171107014824952|
#+-----------------+
With the schema:
df.printSchema()
#root
# |-- requestTime: string (nullable = true)
You can use the techniques described in Convert pyspark string to date format to convert this to a timestamp. Since the solution is dependent on your spark version, I've created the following helper function:
import pyspark.sql.functions as f
def timestamp_from_string(date_str, fmt):
try:
"""For spark version 2.2 and above, to_timestamp is available"""
return f.to_timestamp(date_str, fmt)
except (TypeError, AttributeError):
"""For spark version 2.1 and below, you'll have to do it this way"""
return f.from_unixtime(f.unix_timestamp(date_str, fmt))
Now call it on your data using the appropriate format:
df.withColumn(
"requestTime",
timestamp_from_string(f.col("requestTime"), "yyyyMMddhhmmssSSS")
).show()
#+-------------------+
#| requestTime|
#+-------------------+
#|2017-11-07 01:48:24|
#+-------------------+
Unfortunately, this truncates the timestamp instead of rounding.
Therefore, you need to do the rounding yourself before converting. The tricky part is that the number is stored as a string - you'll have to convert it to a double, divide by 1000., convert it back to a long (to chop off the decimal and you can't use int as the number is too big), and finally back to a string.
df.withColumn(
"requestTime",
timestamp_from_string(
f.round(f.col("requestTime").cast("double")/1000.0).cast('long').cast('string'),
"yyyyMMddhhmmss"
)
).show()
#+-------------------+
#| requestTime|
#+-------------------+
#|2017-11-07 01:48:25|
#+-------------------+